1. Field of the Invention
The present invention relates to an image forming apparatus, in particular an image forming apparatus in which a sheet feed unit is selectively attached to a main body thereof.
2. Related Background Art
Conventionally, examples of image forming apparatuses such as copying machines include those provided with a sheet treatment portion that carries out processes such as bookbinding of sheets. In image forming apparatuses provided with such a sheet treatment portion, there are set modes for performing bookbinding such as a top cover mode and a slip sheet mode. According to those modes, a control is performed so as to insert, for example, sheets contained in a cassette (or sheet feeding trays) provided in an image forming apparatus main body, as a top page (top cover), a last page (back cover), and in-between pages, in addition to sheets on which images have been formed in an image forming portion.
Here, in order to perform bookbinding by using those modes, it is necessary that, other than those sheets on which images are to be formed, top covers, slip sheets, back covers, and insertion sheets are contained in different trays and the order of transport thereof is set such that these sheets including the top covers are subjected to the insertion process at predetermined timings. Note that both the insertion position (place) and the insertion number of the sheets to be inserted at this time can be arbitrarily set.
Then, in the sheet treatment portion, a sheet stack into which the top cover and the like have been thus inserted is subjected to processes such as a stack delivery process, a stitch process, a fold process, and a bookbinding process. Note that an operation mode in which sheets are inserted as a top cover, a slip sheet, and a back cover in this way is herein generically referred to as the xe2x80x9cslip sheet modexe2x80x9d.
Here, at the timing for insertion, those insertion sheets are sent out from the cassette into the same transport path through which the sheets on which images are to be formed passes. Arranged in a middle of the transport path are the image forming portion and a fixing portion. After passing the image forming portion, the insertion sheets pass through the fixing portion. In this case, if color image printing sheets are used as such insertion sheets, there may be a case where the insertion sheets are subjected to heat and pressure upon passing through the fixing portion, resulting in degraded quality of the printed image.
Further, with the recent proliferation of personal computers, color copy paper/color print paper is increasingly used for the insertion sheets. When such color copy paper is inserted, there may be a case where transport property of a sheet feed mechanism is degraded due to oil or the like deposited on the surface of the color copy paper, resulting in a significant reduction in the reliability of sheet transport.
In view of the above, in order to prevent occurrence of those problems, there are proposed image forming apparatuses in which insertion sheets are fed from the downstream side of an image forming portion. As for the method for feeding the insertion sheets from the downstream side of the image forming portion as described above, there is one in which an insertion sheet feeder is provided in a sheet treatment portion and the insertion sheets are supplied from the insertion sheet feeder. Note that apparatuses of this type are described in Japanese Patent Application Laid-Open Nos. 60-180894, 60-191932, and 60-204564.
In each of the apparatuses described in the above official gazettes, as shown in FIG. 5 for example, insertion sheets are supplied at desired timings from an insertion sheet feeder 900 to a sheet treatment portion 500, to be stacked and contained on an intermediate tray 501 provided inside the sheet treatment portion. In addition, sheets delivered from an image forming apparatus main body 800 are also stacked and contained on the intermediate tray 501. Note that, when such an operation is to be performed, it is necessary to set the insertion sheets in advance in a containing portion 900a of the insertion sheet feeder 900, so as to be arranged in page order according to the image content and stacked for the desired number of copy sets.
By the way, the POD (Print-on-Demand) market has been rapidly expanding in recent years. With respect to image forming apparatuses, such rapid expansion of the POD market has created a strong desire for an increase in volume and multi-stage construction of sheet feed trays 802, which are provided to the insertion sheet feeder 900 and to the image forming apparatus main body 800 and contain sheets that are to be fed to an image forming portion 801.
For example, when performing bookbinding, it is necessary to insert preprinted papers, multiple colored papers, tab papers, and the like. However, in the method shown in FIG. 5 in which the conventional insertion sheet feeder 900 is provided in the sheet treatment portion 500, it is difficult to realize multistage construction for the insertion sheet feeder 900. Moreover, the number of the sheet feed trays 802 that can be provided in the image forming apparatus main body 800 was limited.
Accordingly, it is possible to conceive of additionally providing an insertion sheet feeder of a construction capable of containing multiple kinds of sheets as well as a sheet feed unit provided with multiple feed trays. However, with such additional provision of an insertion sheet feeder and a sheet feed unit comes a corresponding increase in the complexity of the overall control and also an increase in cost.
The present invention has been made in view of the above circumstances. Therefore, an object of the invention is to provide an image forming apparatus which is easy to control and can handle POD (Print-on-Demand) while restraining an increase in cost.
According to one aspect of the present invention, an image forming apparatus includes:
an image forming apparatus main body provided with an image forming portion for forming an image on a sheet;
an upstream-side sheet feed unit which is juxtaposed to the image forming apparatus main body and feeds a sheet contained therein to the image forming portion;
a sheet treatment portion for treating a sheet fed thereto; and
a downstream-side sheet feed unit which is juxtaposed between the image forming apparatus main body and the sheet treatment portion and feeds a sheet contained therein to the sheet treatment portion,
in which each of the upstream-side sheet feed unit and the downstream-side sheet feed unit is selectively attachable to the image forming apparatus main body, and the upstream-side sheet feed unit and the downstream-side sheet feed unit have the same construction.
According to another aspect of the invention, an image forming apparatus includes:
an upstream-side sheet feed unit for supplying sheets, an image forming apparatus main body, a downstream-side sheet feed unit, and a sheet treatment portion which are connected in series and arranged in this order from the upstream side of a sheet transport direction; and
main transport paths for sheets, which are each provided in the upstream-side sheet feed unit, the image forming apparatus main body, and the downstream-side sheet feed unit and connected to each other on a substantially horizontal plane, in which:
the upstream-side sheet feed unit includes plural sheet feed trays that contain sheets, and transport paths provided between the sheet feed trays and the main transport path;
the downstream-side sheet feed unit includes plural sheet feed trays that contain sheets, and transport paths provided between the sheet feed trays and the main transport path; and
the upstream-side sheet feed unit and the downstream-side sheet feed unit have the same construction.